The effects of age on continuous learning in the radial maze

Two groups of male Fischer 344 rats were trained in 1 session per day on a series of tasks in a food-reinforced radial maze. The younger group (n = 10) was 3 months old at the start of these experiments; the older group (n = 10) was 21 months old at the start. Following acclimation to the maze, subjects were trained successively on an 8-arm task (8A1) in which entry into all arms was reinforced and a 4-arm task (141) in which only entry into arms 1 through 4 was reinforced. The 8-arm task was then repeated (8A2) and followed by a second 4-arm task (581) in which only entry into arms 5 through 8 was reinforced. The criterion for moving from one task to the next in the sequence was 3 consecutive sessions in which no more than 1 error was made. Comparison of the groups revealed that the younger rats required significantly fewer sessions and made fewer errors before reaching criterion performance in tasks 141, 8A2, and 581. The 2 groups did not differ in their mean rate of responding. The present data indicate that the use of a series of tasks that require continuous learning in a positively reinforced radial maze will permit continued differentiation of young and old rats. This approach may prove useful in the assessment of interventions in the process of age-related cognitive decline.